1. Field of the Invention
This invention relates to a tail gate opening and closing device for a vehicle. Not only a dump truck but also a general type truck are included as a vehicle.
2. Description of the Prior Art
As an example of a conventional tail gate opening and closing for a vehicle, there is a device described in the Tokkaihei No, 6-72357 (Japanese Patent Application No. 72357/1944) which has been already proposed by the applicant. The device of this example is essentially composed, as shown in FIGS. 11 and 12, of a tailgate 3 in which the inner wall surface is formed to have an arcuated shape 3a; a pair of drive cylinders 5 respectively provided at both left and right side walls 4 of the vehicle bed which will be described later; a pair of left and right connection links 8 in which the rear end portions are respectively pivotally supported at both side walls 4 of which the pivotally end surfaces of the connecting links are substantially U-shaped, the inner end portions are pivotally supported at operating (actuating) rods 10 of the drive cylinders 5, and the outer end portions are respectively fixedly provided at left and right side walls 3b of the tail gate 3; tapers 12 are formed by cutting at the lower portions of the inner wall surfaces 11 of the rear end portions of both side walls 4; and taper 1b is formed by cutting at the floor surface 1a in correspondence with the arcuated surface 3a of the tail gate 3.
The device of this example will now be described in more detail. Reference numeral 1 denotes a bed of a dump truck 2. The rear end portion of the floor surface 1a of this bed 1 is formed as a taper 1b.
Reference numeral 3 denotes the tail gate for closing the backward opening portion of the bed. The internal wall surface of this tailgate 3 is formed as an arcuated shape 3a.
Reference numeral 5 denotes a pair of drive cylinders respectively provided at both left and right side walls 4, 4 of the bed. These drive cylinders 5, 5 are pivotally supported through bearing members 7 within recessed portions 6 formed at the side walls 4, 4 of the bed.
Reference numeral 8 denotes a pair of left and right connection links in which rear end portions 8a, 8a are respectively pivotally supported through pivot pins 9 at the both side walls 4, 4 of which end surfaces of the rear end portions are formed substantially U-shaped, the internal end portions of arm portions 8a are pivotally supported at operating rods 10, 10 of the respective drive cylinders 5, 5, and vertical end plate portions 8b provided jointly to the outer end portions thereof are respectively fixedly provided at left and right side wall surfaces 3b, 3b of the tail gate 3. These connection links 8 are somewhat bent in an angular direction with pivot pins 9 being a fulcrum.
The lower portions of inner walls 11 of the rear end portions 4a, 4a of both side walls 4, 4 are cut in correspondence with arcuated surface 3a of the tail gate 3 similarly to taper 1b of the floor surface, and are thus formed as a taper 12. Additionally, reference numeral 13 denotes the truck frame or frame of the vehicle 2.
The operation of the configuration mentioned above will now be described. When operating rods 10 of drive cylinders 5, 5, are contracted as shown in FIG. 11, the tail gate 3 closes the backward opening portion of the bed.
When drive cylinders 5, 5 are driven so that left and right operating rods 10 are extended as shown in FIG. 12, the respective drive cylinders 5 rotate somewhat in a counterclockwise direction. On the other hand, respective connection links 8 begin rotating in a clockwise direction with pivot pins 9 being a fulcrum. At this time, the arcuated surface 3a of the tail gate 3 is in a slide contact with tapers 12 of the rear end portions 4a, 4a of both side walls 4, 4.
When operating rods 10 of the left and right drive cylinders 5, 5 are extended, the tail gate 3 is accommodated (contained) in a horizontal state below the floor surface 1a of the bed 1 through respective connection links 8. As a result, the backward portion of the bed 1 is opened.
The above-mentioned configuration is such that it is possible to open and close the tail gate 3 at any time when desired irrespective of inclination and elevation of the bed 1, that since the driver, etc. is not required to purposely open the tail gate in unloading a load, it is possible to improve the work for discharging the load (loaded material), so that the vehicle can move in the state where the tail gate 3 is accommodated (contained) in a horizontal state below the floor surface 1a of the bed 1, and the like. However, since the loaded material is directly in pressure contact with the arcuated internal wall surface of the tail gate, there are drawbacks such that earth and sand, etc. may be attached on the internal wall surface after discharging a load, and/or the lower portion of the internal wall surface 3a of the tail gate 3 may be damaged in dependency upon the loaded material.